Sensor for monitoring for the presence and measurement of aqueous aldehyde biocides

ABSTRACT

An analytical system and method for periodically monitoring an injection water distribution pipeline for the presence and concentration of formaldehyde or other aldehyde-functional biocide includes pumps, one of which provides a predetermined volume of injection water drawn from the pipeline at a sampling point and the other a predetermined volume of a reagent, preferably a buffered solution of dimedone, from a reagent storage vessel which are mixed and then heated in a chamber to a predetermined temperature to promote formation of any reaction products. The heated reaction mixture is passed to a detection cell and exposed to light of predetermined wavelength which, in accordance with the Hantzsch reaction, molecules having an aldehyde functional group that reacted with dimedone produce a fluorescence-emitting reaction product, the intensity of which is measured and compared to data previously obtained from standard aldehyde-containing solutions.

FIELD OF THE INVENTION

This invention relates to the continuous monitoring for the presence andmeasurement of the concentration of aldehyde biocides in aqueoussystems.

BACKGROUND OF THE INVENTION

In oil exploration and production fields, seawater is pumped intostrategically positioned injection wells to enhance the recovery of oilfrom the reservoir. The recovery of oil requires injection of water intooil-bearing reservoir rock in order to move the hydrocarbons to aproduction well where they can be produced to the surface. The length ofthe pipeline from the source of the water to the oil field where it isto be injected can be thousands of kilometers. The residence time ofwater in the pipelines can be significant and the likelihood of thepresence of conditions that promote bacteria growth is extremely high.The growth of bacteria in the pipeline can be prevented or greatlyinhibited by the addition of a biocide at the water intake point thatwill have the effect of inhibiting bacterial growth throughout thepipeline.

The distribution pipelines normally form a grid to supply water to anumber of injection wells in the vicinity of the production wells.Because of the overall length of the pipeline system, a drop in theeffective concentration of biocide can occur at the point of use. Thereduction in biocide concentration is due to the degradation of theactive ingredient(s) present in the biocide formulation. Hence, it isimportant to know the actual concentration of biocide present in waterat the point of use.

Biocides are also commonly added to water used in cooling towers andsimilar industrial systems to combat growth of bacteria. For mostcooling tower installations, the degradation of the biocide is not anissue since the pipelines used with the cooling tower are not of greatlength; hence the concentration of biocide added remains almost constantthroughout the cooling tower system. Generally, the addition of abiocide, or biocides to a distribution pipeline is at the main waterintake point. For pipelines, the quantity added at the initial injectionpoint is dependent upon the flow rate of water, ambient pipelineconditions and the length of the pipeline. The customary biocidetreatment method for the biocide addition to an injection water streamis not continuous; rather, the biocide is added into the water systemperiodically on a fixed schedule that has been determined based onexperience.

Many commonly used industrial water treatment biocide formulationscontain formaldehyde and/or other compounds having an aldehydefunctional group as the active ingredient to combat the growth ofbacteria. After the addition of a predetermined amount of biocide over aprescribed time period (commonly referred to as a “slug”), a watersample is collected manually at various downstream sampling points andthe samples are taken to a laboratory where any of a number of knownanalytical methods can be used to detect the presence and determine theconcentration of any biocide in the sample of injection water. Once thesamples have been received, the laboratory generally requires severalhours to report the concentration of any biocide present in the watersystem. This practice is followed on a regular basis and after theaddition of biocide into seawater at the point of water intake. Thismethod of analysis is time-consuming and is not always practical atremote locations along the pipeline. Due to the complexity of some waterinjection networks in large oil fields, including those comprised ofremote locations, the water distribution system cannot be effectivelymonitored by personnel at the sites for treatment and measurement ofresidual biocide concentration. Additionally, due to the high volumetricflow of water and pipeline length, it is often difficult to preciselydetermine when the biocide slug will arrive at the water sampling point,leading to a missed opportunity.

The problem addressed by the present invention is the monitoring ofbiocide in a stream of injection seawater on a continuous basis. Anotheressential aspect of the problem is to determine the concentration ofbiocide in the water system at the point of use, and at interim samplingpoints in real-time, utilizing means capable of determining the presenceand also recording the concentration of the active ingredient, e.g.,formaldehyde and/or other aldehyde functional groups.

Currently, there is no method or apparatus commercially available forthe continuous monitoring for the presence of a biocide in an aqueousmedium and no commercially available analyzer system that automaticallysamples, detects and measures the concentration of aldehyde-functionalbiocides in seawater injection distribution systems.

There is a need for in-line and real-time sensing devices for continuousmonitoring of biocidal chemicals in these geographically extensive andcomplex water distribution systems. A system in which such testinformation is recorded and that is able to transmit the data fromremote locations to personnel responsible for the system is needed.

SUMMARY OF THE INVENTION

The above problems are resolved and other advantages are provided by themethod and analytical system of the present invention, which comprehendsan in-line system that includes a sensor and analyzer assembly thatcontinuously monitors for the presence and measures the concentration ofany aldehyde-containing biocide detected in injection water streams, andin industrial and waste water streams. The in-line system is equippedwith a microprocessor/controller which transmits test data to an offsitecontrol center, allowing for the monitoring of aldehyde-containingbiocide in remote pipelines. As used herein, the term“aldehyde-containing biocide” includes a biocidal composition containingformaldehyde and/or one or more aldehyde functional groups that reactwith dimedone.

An automated system is provided for indicating the presence andconcentration of the biocide by incorporating the reaction of aldehydewith dimedone to monitor the seawater injection system for the presenceof biocide. The sensor and analyzer assembly includes a combination offlow pumps, an injection valve, a mixer, a heating chamber and anoptical detection cell.

The detection of the aldehyde and/or aldehyde functional group utilizesthe chemical reaction of a reagent with a biocide that contains analdehyde group. The primary mechanism for detection is the Hantzschreaction in which molecules having an aldehyde functional group reactwith dimedone in the presence of a buffering agent such as ammoniumacetate, to produce a reaction product that is fluorescent. The Hantzschreaction mechanism can be represented as follows:

A buffer is preferably added to maintain the pH of the reaction mediumat about 4.5. It is possible to use other buffering agents to maintainthis pH value.

Although the rate of reaction and formation of the fluorescent productis relatively slow at room temperature, the rate is accelerated byincreasing the temperature of the reaction medium. The product formedproduces high levels of fluorescence at temperatures in the range of 80°to 90° C.

The reaction between formaldehyde and dimedone differs from the reactionof acetaldehyde or glutraldehyde with dimedone since the reactionproducts formed may fluoresce at slightly different wavelengths. It hasalso been found that different aldehyde molecules produce differentlevels of fluorescence in their reaction with dimedone. When differentaldehydes are present in the biocidal system added to the seawater, thedetection system requires a calibration curve that is specific for eachof the aldehydes.

The purpose of the buffering system is to maintain the pH of thereaction media at about 4.5, because it has been found that the productformed at a pH of approximately 4.5 shows a higher level of fluorescencewhen other conditions, e.g., temperature, are held constant.

A buffering agent is not required in order for the Hantzsch reaction toproceed, but it is preferable to operate at this pH, particularly inorder to more effectively detect the presence of low levels of biocidein seawater and to assure that the reaction goes to completion. Thebuffer solution helps to maintain the response for the relatively lowerconcentrations of biocide that may be present in the seawater injectionsystems.

In the absence of a buffering agent, the reaction is slow and thedetection of a biocide in the seawater is also slowed, resulting in verya broad peak. Additionally, the response is not readily reproducible inthe absence of a buffer.

In addition to ammonium acetate, another suitable buffer includes amixture of potassium hydrogen phthalate and sodium hydroxide. The buffercan be added as an aqueous solution. The concentration of the bufferagent can be in the range of a pH of 4.0 to 5.0.

It has been noted that the presence of minerals in the seawater does notaffect the response.

In the apparatus of the invention, the aqueous sample that is to betested for the presence of a biocide with an aldehyde functional groupand the dimedone reagent are maintained in separate containers.Predetermined quantities of the aqueous sample and reagent are withdrawnby separate pumps, mixed, and then heated in a vessel or chamber to thedesired temperature; thereafter, the heated reaction product is exposedto light from a lamp of predetermined wavelength in a detection cell.The wavelength of the light can range from about 380 nm to 480 nm.

The detection cell can be constructed from readily-available componentsas a two-part assembly that includes a chamber fitted with a transparentwall or window for receiving the flowing mixture and a second chambercontaining the sensor of the optical detection device which is isolatedfrom the liquid containing the reaction product by the transparent wall.The limiting reactant in this reaction scheme is the molecule containingan aldehyde functional group. The signal produced by the opticaldetection probe is directly proportional to the amount of reactionproduct formed in the reaction of the aldehyde molecule and dimedone,which in turn is directly proportional to the amount of aldehyde presentin the sample being tested.

Different manufacturers and suppliers of the biocidal water treatmentcompositions utilize different types of aldehydes, includingformaldehyde, acetaldehyde and glutraldehyde. The method and system ofthe invention are capable of detecting the presence of any moleculecontaining a —CHO functional group. The sensor system is firstcalibrated by testing aqueous samples containing predetermined knownconcentrations of an aldehyde. Once calibrated, the sensor can beutilized to monitor for the presence of the known aldehyde and tomeasure the concentration of any known aldehyde in the aqueous sampleswithdrawn from the pipeline sampling points. The sensor system ispreferably automated for analysis of samples that are periodicallywithdrawn from a remote pipeline, the principal limitation of the systembeing the availability of a supply of the dimedone reagent and knowledgeof the type of aldehyde added to the seawater.

The advantages provided by the present invention include:

-   -   a. enhancing the reliability of an established injection water        treatment program by the timely detection of biocide residuals        and adjusting upstream operating parameters and conditions        accordingly to provide adequate control of any bacterial        activity in the system;    -   b. minimizing potentially serious and costly downhole bacterial        growth problems resulting from the depletion of biocide in a        geographically extensive seawater distribution system and        enhancing the effectiveness of bacterial control and the water        quality in remote areas; and    -   c. avoiding the addition of an unnecessary excess of biocide to        the injection water system thereby achieving cost savings and        reducing the amount of biocide used.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below and withreference to the attached drawings in which the same or similar elementsare referred to by the same number, and where:

FIG. 1 is a schematic diagram of a sensor/analyzer system that includesflow pumps, an injector, a loop mixing chamber, a heater module, anoptical sensing device for continuous and regular monitoring for thepresence of an aldehyde-containing biocide in an aqueous system, and amicroprocessor/controller equipped with a transmitter and antenna usedto transmit data from the optical sensing device to an offsite controlcenter that is equipped with a receiver/transmitter and antenna toreceive the transmitted data and that is linked to a separatemicroprocessor/controller;

FIG. 2 is a schematic diagram of an optical detection cell suitable foruse in the analyzer system of FIG. 1 to detect any fluorescenceemanating from a biocide reaction product;

FIG. 3 is a process flow chart of the automated sampling process inwhich the system analyzes samples on a substantially continuous basis atprescribed intervals when biocide is present in the sample and changesto a standby mode with less frequent sampling and analysis when thebiocidal compound is no longer detected; and

FIG. 4 graphically depicts a peak-by-peak response to the presence of abiocide in samples taken from a seawater injection system feedstream.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the system and method of the present invention aredirected to a chemical reaction product-based analyzer for regularlymonitoring the flowing stream of injection water for the presence andconcentration of formaldehyde and/or other aldehyde functionalbiocide(s). The system is configured and operated to monitor for thepresence of an aldehyde-containing biocide in an aqueous medium withouthuman intervention. The automated system is based on the reaction of thealdehyde and reagent which are mixed and heated to a predeterminedtemperature to produce an optically detectable fluorescence when exposedto a known wavelength of light.

The analyzer includes two pumps, one of which provides a predeterminedvolume of injection water drawn from the pipeline at a sampling pointand the other delivers the reagent, e.g., dimedone, from a reagentstorage vessel. In a preferred embodiment, peristaltic pumps are usedfor delivery of the liquids at a constant rate. It is also preferred tomix the buffer solution with the dimedone reagent so that the buffersolution is delivered as a single stream by the pump. The output fromeach of the pumps is introduced into a mixing chamber to provide auniform mixture and then heated to a predetermined temperature, as willbe explained in more detail below. The mixing and heating steps can becombined in a single vessel. Heating the reactant produces a chemicalproduct which fluoresces at a known wavelength. The fluorescent liquidis passed through a detection cell equipped with a fiberoptic pick-upprobe that receives the light waves. The volume of injection watercontaining the reacted aldehyde moiety is controlled using an injectionloop downstream of the flow pump. Sufficient time is allocated to insurethat all the aldehyde present in the injection loop has reacted with anexcess of dimedone to produce the fluorescent reaction product. The loopaccommodates all of the seawater sample mixed with the buffered dimedonesolution. The amount of aldehyde in the seawater is the limitingreactant so that all the biocide that may be present in the seawatercompletely reacts with dimedone reagent.

The analyzer is pre-calibrated using a known concentration of analdehyde in a volume of liquid equivalent to the volumetric capacity ofthe loop. The response is preferably recorded in the form of the totalarea under the produced peak. Following calibration, the analyzer isplaced in the sample analysis mode. The software used in the system isbased on a generic product such as a visual basic program used inconjunction with LabVIEW software. The program can be prepared by aprogrammer of ordinary competence.

The detection cell is calibrated by reacting a predeterminedconcentration of aldehyde with the reagent and the intensity of thefluorescence produced is measured by optical means and converted by thesoftware into a graphic display and/or tabular data. The area under thepeak is measured and a response factor is calculated. A plurality ofsamples over an appropriate range of varying concentrations that can bedetermined by experience are preferably prepared to establish thefactors. For example, the calibration curve is obtained by preparing aknown concentration of formaldehyde in water and its value is kept closeto the experiential levels of formaldehyde present in the seawaterinjection system. Two different sample standards can be prepared; one atabout 200 ppm of formaldehyde in water and the other at about 700 ppm tocover the high and low ranges of the desired concentration of biocidepresent in the seawater injection system. In the case of a water samplecontaining the biocide reaction product, a similar peak is generated.The area under the peak and the response factor determined in thecalibration step is used to calculate the amount of biocide present inthe sample of injection water drawn from the pipeline.

In the practice of the method of the invention, the sample of watercontaining an aldehyde functional group reacts with the dimedone reagentto produce molecules which fluoresce at the wavelength of the lightsource in the detection cell. The emitted light is gathered in the fiberoptic probe and transmitted to a sensor in the optical detector. Thesignal from the optical detector is transmitted to a suitably programmedmicroprocessor known in the art. The output signal from themicroprocessor operates a graphic plotter and is translated into a peakfrom which the concentration of aldehyde present in the flowing sampleis calculated. The data is transmitted to an offsite control centerwhere it is displayed on a monitor and/or printed for review by atechnician. All data is entered for retention in an associated suitablestorage medium. In the event that separate analyzers are utilized formany different sampling points in the distribution system, it ispreferred that a dedicated set of calibration curves be developed andused with each analyzer. The detection cell can be constructed fromcommercially available parts and was designed specifically for this newapplication.

The optical detection cell operates on the basic principle of theBeer-Lambert Law which states that there is a logarithmic relationshipbetween the transmission, or transmissivity, T, of light through asubstance and the product of the absorption coefficient of thesubstance, α, and the distance the light travels through material, i.e.,the path length, l. The absorption coefficient can, in turn, be writtenas a product of either a molar absorptivity, or extinction coefficientof the absorber, ε, and the molar concentration, c, of the absorbingspecies in the material, or an absorption cross-section, σ, and thedensity N′ of absorbers.

The amount of sample selected for predetermined injection is based onthe volume of the sample loop. A loop having a relatively larger samplevolume will produce a stronger signal and will be capable of accuratelymeasuring relatively lower concentrations of an aldehyde biocide in theaqueous sample by producing a larger area under the peak. It will beunderstood that once the analyzer is calibrated for one, but preferablya plurality of specific calibration concentrations of aldehyde in thewater sample, the same volumetric loop size is maintained for theanalysis of subsequent test samples. The loop/detection cell is flushedout with seawater between sample tests to eliminate any fluorescentreaction product and dimedone carry-over from the previous analysis andto prevent blocking of the sample lines with salt deposits from theseawater.

The operation of the analyzer is preferably controlled by a suitablyprogrammed microprocessor so that it can operate without humanintervention after it has been installed in the field. In a preferredmode of the practice of the invention, a plurality of analyzers areinstalled along the water injection distribution system in the field forsubstantially continuous monitoring for the presence and determinationof the concentration of biocide at different locations in the pipelinesystem. The microprocessor control system can utilize dedicated softwarethat operates the analyzer in three modes, i.e., (a) continuous orfrequent mode; (b) a slug or intermittent detection mode; and (c)calibration mode. It will be understood that the use of the term“continuous” is relative and that the time between tests is limited bythe time required to initiate sampling, process the sample, and collectthe data from any fluorescence detected. However, when compared to priorart methods and procedures which required collected samples to becarried to a laboratory, the present method is aptly characterized ascapable of substantially continuous monitoring with the reporting ofresults in real time.

Example of Analyzer Operational Mode

The following sequence describes an embodiment for automated operationof the system. The dedicated software initiates sampling of the pipelinein the intermittent or slug detection mode. Sampling is initiated basedon a predetermined schedule, e.g., once every hour, and an analysis isperformed. The frequency of injection can be changed based uponexperience with the particular system, location and number of samplingpoints, the number of injections required and the volume of the reagentreservoir available for use in the analyzer. If no biocide reactionproduct is detected during the analysis, the sampling continues in theintermittent mode. If a biocide reaction product peak is detected, thesoftware switches to sample analysis mode for the next run. In sampleanalysis mode, a sample injection occurs every seven minutes for as longas some product is detected. The biocide concentration is determined bya factor provided by user input. The compositional information is of aparticular biocide provided by the supplier in the MSDS or othercommercial literature or product labels. The concentration offormaldehyde or other aldehyde-containing compounds present in eachformulated product can vary based on the manufacturer or supplierspecification. If no biocide peak is detected following a sampleanalysis, the software returns sampling to the plug flow or intermittentdetection mode. This mode of operation minimizes the use of reagent whenno aldehyde group has been detected.

The operation of the analyzer is not affected by temperature variationdue to the fact that the chemical reaction proceeds at a predeterminedtemperature that is much higher than ambient temperatures so that evensignificant variations in ambient temperature, e.g., in desert andarctic environments, will have little or no effect on the outcome andthe accuracy of the analysis. This represents a significant advance inthe art of providing real-time results from remote locations withminimal human intervention.

In a preferred embodiment, the analyzer is used in conjunction with asolar powered energy source connected to one or more storage batteriescapable of providing sufficient electrical power to operate themicroprocessor, pumps and heating system in locations that are remotefrom an established power grid.

The analyzer is initially calibrated using known concentrations ofaldehyde-containing biocides that produce a fluorescence, the magnitudeor intensity of which is detected by the optical sensor and converted toa corresponding data entry that is stored in the memory of themicroprocessor with the sample concentration and other relatedinformation for reference during subsequent injection water sampletesting. If changes are made to the type or supplier of the commercialbiocides, the new products should be subjected to the same calibrationsteps and the resulting data entered into the memory of themicroprocessor associated with the analyzer for reference duringinjector water sample testing.

The apparatus is calibrated in this way using varying concentrations ofdifferent biocides of the type that are used in the injection waterdistribution system. As will be understood by those of skill in the art,this calibration data set can be used with an apparatus that ismanufactured using the same components and a consistent design. Anychanges in the configuration of the components, optical sensor and thelike may necessitate the preparation of a new set of calibration datafor storage and reference in the memory of the associate microprocessor.

Description of a Preferred Embodiment

Referring now to FIG. 1, the biocide analyzer system (1) includesinjection water sampling tube (6) which is in fluid communication with asampling point in a section of an injection water distribution system.Tube (6) delivers injection water containing biocide through injectionwater valve (8) to the sample or calibration solution reservoir (10). Itwill be understood that the sampling procedure is also applicable to thepreparation of the calibration data from known concentrations ofcommercial biocides of the type customarily used in the injectionseawater system.

A sample pump (14A) is connected to sample or calibration reservoir (10)by sample delivery conduit (13) and a predetermined quantity of theinjection water sample that is to be tested for biocide is injected intothe system through injection valve (15). Reagent from reagent storagereservoir (11) is carried via conduit (12) to reagent pump (14) anddownstream conduits (17, 19) to be mixed with sample water which maycontain biocide in mixing vessel (20). The mixed sample is transferredvia transfer conduit (20) to the heating vessel (23) where the sample isheated to a predetermined temperature at which the rate of reaction isaccelerated in order to increase the rate of formation of any of thefluorescent reaction product. After a predetermined period of time thatis sufficient to substantially complete the reaction of any aldehydepresent, the reaction mixture is introduced via heated sample conduit(22) into optical detection cell (24), where it is exposed to the lightof the lamp (30) and any fluorescence of the reaction mixture (28) isdetected and measured by sensor (40). After the measurement has beencompleted and recorded, the liquid (28) is passed through dischargeconduit (26) and collected as waste in a reactant product storagechamber (27).

The fluorescence intensity measurements are recorded by the programmedmicroprocessor/controller (50), which receives the measurements viaconduit (32), and then transmitted in real time to an offsite controlcenter (70) via transmitter (60) and antenna (62). The offsite controlcenter (70), utilizing a microprocessor (80) equipped with a transmitter(90) and antenna (92), receives the real time fluorescence intensitymeasurements via signal (34). The fluorescence measurements are analyzedat offsite control center (70) and any necessary adjustments to thebiocide treatment process can be determined with the aid ofmicroprocessor/controller (80) and communicated to field personnel toadjust the biocide addition schedule.

The optical measurement cell (24) is described in more detail withreference to FIG. 2, and in the embodiment illustrated is comprised of aflow cell (233) and a sensor portion (250). The mixture of reactionproduct, liquid sample and excess reagent (239) enters the flow cell(233) through an inlet (230) and fitting (232). The liquid is passedthrough chamber (234) where it is exposed to the light emitted by thelamp (30). A silicone spacer (236) is placed over the detection cell(250). The liquid is retained in the chamber by a sheet or web (237) ofchemical-resistant transparent plastic material. The sensor-receivingportion (250) of the detection cell is secured to the flow cell (233)with suitable fasteners (252). The liquid (239) flows out of the flowcell through fitting (232) and outlet (231). The flow cell (233) isconstructed of a chemical-resistant material such as polytetrafluoroethylene (PTFE), and the sensor portion (250) is constructed of eitherPEEK or PTFE. The fiberoptic probe (40) is inserted in sensor channel(256) with its receptor end in position opposite the flow line (238),which has been exposed to the light of the lamp (30) to detect anyfluorescence resulting from the above-described reaction. Following eachtest, the loop is flushed with seawater to prevent carry-over of anyreagent and to prevent the build-up of solid salt minerals.

FIG. 3 is a process flow chart of the method of operation. Followinginstallation of the analyzer at a sampling point, the start-upprocedures (301) include the filling of the reagent storage vessel,confirming the charged status of the storage battery and operability ofthe solar collection device, proper functioning of the pumps, mixingdevice and heater, and installation of the software, including storagein its associated memory of the calibration data that will be used todetermine the concentration of the aldehyde reaction product for actualseawater samples during the tests. In the event that an error ormalfunction is detected, the microprocessor transmits an alert messageor alarm to the maintenance personnel for appropriate action.

Sampling is initiated (302) either by a manual switch actuated bypersonnel at the site or remotely via transmission of a signal to areceiver/transmitter associated with the analyzer. Once activated, theanalyzer operates in a substantially continuous mode requiring no humanintervention.

In a preferred embodiment, the system checks for the presence ofadequate reagent to continue the testing protocol (312). This step canalso include generation of a warning signal indicating a predeterminedlow level of reagent in the storage vessel. In either of these events,e.g., low or no reagent detected, a signal will be transmitted to theappropriate maintenance personnel to alert them to the condition. Wherethere is adequate reagent to proceed, the system checks to see if thealdehyde reaction product was detected in the last sampling (304) and ifso, a peak is produced. Once the peak is produced, its detection causesa signal to be generated in the microprocessor. The analyzer continuesto run and analyze samples on a predetermined continuous frequentsampling protocol (310), e.g., every five to ten minutes until there isno biocide reaction product detected. In the event that no biocidereaction product is detected (304), the analyzer proceeds to theintermittent sampling protocol (306), e.g., sampling every 60 minutes inorder to reduce consumption of reagent. Again, the availability ofreagent is checked (308), and if sufficient reagent is available forcontinued testing, the intermittent sampling protocol continues to checkfor the presence of biocide reaction product (304). The intermittentsampling protocol continues so long as there is no reaction productdetected; once reaction product is detected, the frequent samplingprotocol cycle as described above is initiated and continues until nofluorescence from a reaction product is detected, after which the systemreturns to the intermittent sampling protocol.

In both modes of operation, the condition of low or no available reagentresults in an appropriate signal being sent to bring this condition tothe attention of maintenance personnel (349) and thereafter the systemshuts down (350) pending appropriate maintenance actions. In a furtherpreferred embodiment, basic system checks are routinely performed toconfirm that the various elements are functioning within predeterminedoperational parameters. This would include the determination of batterystatus, power received from the solar energy collection device, loadmeasurements on the pumps during operation, and the like. Appropriateaction must also be taken in setting up the apparatus in order toaccount for special environmental conditions, e.g., sand storms inremote desert locations and snow in arctic areas that will interferewith the solar energy collection device. Procedures and means fordealing with these environmental issues are known and available for usewith the system of the invention and need not be elaborated here.

FIG. 4 is a graphic representation of multiple injection responses for150 ppm of formaldehyde in demineralized water. The response plotted isrepresentative of a biocide present as a slug in the seawater injectionsystem. The graph depicts the continuous response of the analyzer forthe presence of the biocide. The x-axis represents the number ofinjections and the y-axis is the detector response and is in arbitraryunits. The baseline at 1610 is an arbitrary number associated with theparticular detector cell employed in this series of tests. While thebaseline is arbitrary, it should be stable from one injection to anothersince a stable baseline for multiple injections indicates that theanalyzer is operating properly.

This invention can be applied to a plurality of remote sampling pointsand provides a sample handling system in which data can be collected,stored and most importantly, transmitted electronically to the engineersand technicians responsible for maintaining the seawater treatmentsystem. The following detailed steps illustrate the method of operationof an embodiment of the present invention:

-   -   1. A freshly prepared biocide standard sampling line is        connected to the inlet of the analyzer. A built-in peristaltic        pump moves water to fill the injection loop and remaining water        is discharged as waste. A second pump continuously introduces        the reagent through a second line. Reagent and water containing        biocide are metered into a mixing vessel and thereafter the        mixed solution is heated to approximately 90° C. The heater is        designed to heat the specific volume of the vessel to a        temperature for optimum reaction conditions and the mixing and        heating steps can be performed in a single vessel. In an        illustrative embodiment shown in FIG. 2, the reaction vessel is        constructed from a polyether ether ketone (PEEK) cylinder that        contains in its core a 130 cm coil of PTFE tubing having an        internal diameter of 0.7 mm and an internal volume of 0.5 ml.        This reaction coil is enclosed in a heat-resistant isolation        jacket formed from meta-aramid paper (tradename NOMEX) and        polyimide tape (tradename KAPTON). On the outside of this jacket        is coiled 325 cm of resistive wire (Mn—Ni, 11.8 Ω/m, 80 micron        core from AB Kanthal, Sweden). The power rating of this        resistive heater is 15 W at 24 VDC. The coiled jacket is secured        with polymide tape and inserted into the PEEK cylinder housing.        The completed assembly is insulated with rigid polyurethane        foam.        -   The resistance heating coil of the reaction chamber is            controlled by a commercially available            proportional-integral-derivative (PID) temperature            controller that is connected to the heater coil through a            power metal-oxide semiconduction field-effect transistor            (MOSFET) circuit which is driven by the SSR output of the            PID. The temperature measurement is performed with a            resistance thermometer, such as a PT100 probe, that is            connected to the PID temperature input.        -   The heated mixture is introduced into the optical detection            cell. In the optical cell, any fluorescence produced by the            exposure to light source is detected, and if present, the            intensity of the fluorescence is measured; a comparison of            the test sample values is made to the values of calibration            samples stored in the memory associated with the analyzer's            microprocessor; the concentration of aldehyde in the test            sample is then recorded. The concentration of the reaction            product is directly related to the concentration of the            aldehyde functional group of the biocide.    -   2. The value of the area under the peak is calculated and        recorded by the processor and a response factor is automatically        calculated. A log of readings is entered in the associated        memory device as a permanent record.    -   3. The injection seawater line containing biocide is connected        to the sample inlet. Water is allowed to flow through the        injection loop and the procedure of step 1 is repeated to record        the value of the peak area. The peak area value and the response        factor as was calculated in step 2 are recorded for the seawater        sample.    -   4. The peak area and the response factor calculated in step 2        are used to calculate the amount of biocide present in water        based on the sample peak area value.    -   5. Further, the seawater samples are periodically admitted for        analysis, e.g., every 7 to 10 minutes for as long as biocide is        detected in the samples. This is referred to as the continuous        or frequent sampling mode.    -   6. If no biocide is detected in a seawater sample, the system        processor resets to sampling of the injection water pipeline at        sixty-minute intervals. This is referred to as the intermittent        detection or monitoring mode.

The analyzer system is capable of measuring 20 to 2000 ppm of biocidethat contains aldehyde-based active ingredients present in an aqueoussystem, e.g., biocidal-treated seawater.

The following analytical data was obtained from field studies using themethod and apparatus of the invention described above. The readings inTable 1 are parts per million (ppm) of a residual biocide identified asproduct TK-1415 as detected by the aldehyde analyzer in samples oftreated seawater intended for use in injection wells.

TABLE 1 SENSOR READINGS (Biocide TK-1415) TIME (hr/min) CONC. (ppm)14:50 198 16:01 1412 16:12 1514 16:22 1452 16:32 1385 16:42 1350 16:521249 17:13 789 17:23 1210 16:33 196

The data in Table 2 are readings taken at varying time intervals for adifferent aldehyde-based biocide identified as product TK-1420. Thesedata are for two different formulations of biocidal compositionscontaining different amounts of the active ingredient.

TABLE 2 SENSOR READINGS (Biocide TK1420) TIME CONC. REMARKS 05:37 PM 14107:19 PM 347 07:29 PM 210 07:39 PM 144 09:21 PM 147 09:42 PM 171 10:53PM 212 12:15 AM 278 12:25 AM 195 01:16 AM 231 01:26 AM 223 01:47 AM 16602:48 AM 203 03:29 AM 237 04:50 AM 194 05:01 PM 207 06:58 PM 301 12:35AM 168 03:38 AM 213 05:00 AM 200 07:13 AM 175

From the above description, it will be understood that the analyzer ofthe invention provides a system and method to detect the presence andthe concentration of an aldehyde-based biocide in a water system on anessentially continuous sampling basis. The analyzer functionsindependently of the temperature, flow rate and pressure of the streambeing sampled. The chemical reaction between the active aldehydeingredient present in the biocide and the reagent produces a fluorescentmolecule at the operating temperatures. The mode of operation of theanalyzer is based on measurement logic. In order to maximize the timefor the uninterrupted operation of the analyzer in the field over anextended period of time, it functions to take samples for frequenttesting only when the biocide is likely to be present in the flowingstream of water. If no biocide is detected in water, the analyzerdecreases the frequency of sampling and testing. This feature allowsconservation of stored reagent in the analyzer system and prolongs thetime over which the system can operate before reagent must bereplenished. The data is routinely transmitted to operations personnelin real time who can then take appropriate steps to maintain the levelof chemical addition at the intake point that is necessary to meet therequirements established for the use of the injection water in thefield.

The system and method of the invention have been described in detailabove an in the attached drawings; however, modifications will beapparent to those of ordinary skill in the art from this description andthe scope of the invention is to be determined by the claims thatfollow.

The invention claimed is:
 1. A method for the detection, measurement andrecording in real time of the concentration of any aqueousaldehyde-based biocidal compounds present in water flowing in a conduitat a sampling point, the method comprising: a. withdrawing a sample ofthe water from the conduit at the sampling point; b. forming a reactionmixture of a predetermined volume of the aqueous sample and apredetermined volume of a dimedome reagent having a pH in the range offrom 4.0 to 5.0 that produces a fluorescent reaction product whencontacted with an aldehyde or aldehyde functional group; c. heating thereaction mixture to a predetermined temperature to increase the rate ofreaction between the reagent and any aldehyde functional groups presentin the aqueous sample; d. exposing a predetermined volume of thereaction mixture to a light of a wavelength known to produce visiblefluorescence of an aldehyde-based reaction product; e. opticallymeasuring the intensity of any fluorescence detected and determining andrecording the measured value; f. comparing the measured value of theintensity of any fluorescence produced to the measured values ofcalibration samples of known aldehyde concentrations; and g. reportingthe concentration of any aldehyde-based biocidal compounds in theaqueous sample as undetected or at a concentration corresponding to thatdetermined from the comparison of the aqueous with the calibrationsamples.
 2. The method of claim 1 in which the aqueous sample andreagent are mixed in the presence of a buffering agent.
 3. The method ofclaim 2 in which the buffering agent is selected from the groupconsisting of ammonium acetate and a mixture of potassium hydrogenphthalate and sodium hydroxide.
 4. The method of claim 2 in which thebuffering agent is present in an amount sufficient to maintain a pH ofabout 4.5.
 5. The method of claim 1 in which the temperature to whichthe reaction mixture is heated is a predetermined temperature that issufficiently higher than the ambient temperature so that significantvariations in ambient temperature will have no significant effect on theoutcome and accuracy of the analysis.
 6. The method of claim 1 in whichthe reaction mixture is heated to a temperature in the range of 80° C.to 90° C.
 7. The method of claim 1 in which the reaction mixture isexposed to light with a wavelength in the range of 380 nm to 480 nm. 8.The method of claim 1 in which the aldehyde-based biocidal compoundsinclude formaldehyde, acetaldehyde and glutaraldehyde.